I don't understand the "levels". Could you explain to me why there are levels and what each one does?
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DougJul 5 '12 at 0:51

Run levels are a way to keep multiple boot "configurations" available on your box. Typically I have a run-level for a graphical login and another for a text login, although it's really up to you whether you use more than one (or what you keep configured in each run level). This DebianHelp article will do a better job than I would describing run levels from scratch
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Mike PenningtonJul 5 '12 at 0:56

You could try installing rcconf via aptitude. It lists services that are started on boot. Rcconf will list all installed services -- services that start on boot are clearly marked. To run rcconf simply run rcconf as root.